1. Field of the Invention
The present invention relates to a method and a device for obtaining information relative to a given material, organic or mineral, likely to be contained in geological formations and in particular those passed through by a bore hole. With the present invention, more especially, the presence of certain materials in geological formations can be detected and the quantity of these materials may be possibly determined.
2. Description of the Prior Art
Up to the present time, the presence of certain materials, contained in geological formations, was indicated by the results of analyses made on samples of these geological formations, taken by special apparatus of the core barrel type, or coming from excavations material collected during drilling of these formations.
These analyses, which are for example chemical analyses or else analyses of the products resulting from the pyrolysis or the oxidation of the sample, are carried out at the surface and are relatively long to put into effect, since the most rapid require at least ten minutes or so per sample.
The prior art may be illustrated by the French Pat. Nos. 2.120.638 and 2.424.551, U.S. Pat. Nos. 4,317,993 and 3,665,195 as well as the following articles published in the "Canadian Journal of Physics":
article by R. A. COWLY entitled "Inelastic scattering of thermal neutrons from liquid helium" (Volume 49, No. 2 of the Jan. 15, 1971, Ontario (CA), pages 177 to 200), and
article by J. R. D. COPLEY entitled "Crystal dynamics of rubidium. 1. Measurements and harmonic analysis" pages 657 to 675.
Experiment No. 9.06.327 mentioned in the 1980 annual report of the Institut Laue Langevin de Grenoble - France, with the title "Investigation of the vibrational state of butane adsorbed on graphite at low and high energy transfers", has shown that the incoherent inelastic diffusion spectrum of neutrons interacting with a layer of butane of a given thickness, adsorbed on a CARBOPACK.B (commercial trademark) graphite support medium, presents peaks in the vicinity of certain energy levels among which some are characteristic of the vibrations of the C--H pair, of the C--C pair and of a swinging movement of the group CH.sub.3.
The present invention, whose aim is to allow rapid determination of the presence of certain materials in the geological formations through which a bore hole will pass, is based on the fact that the authors of the present invention have discovered similar phenomena in the incoherent inelastic diffusion spectrum of neutrons of a geological formation subjected to a flow of neutrons having a given energy level.
It is possible, according to the invention, to rapidly identify and/or determine the quantity of certain materials contained in geological formations. It is also possible to obtain other information concerning these formations, for example their hydrogen atom density.
An apparatus for carrying out measurements on geological formations passed through by a bore hole has been designed. These measurements are advantageously carried out at different levels in the bore hole so as to determine, depending on the depth and practically continuously, the ground zones where the desired material is present.
The recent experiment mentioned above was carried out on a given material, in this case butane, which was adsorbed on a special graphite support medium made from CARBOPACK.B (commercial trademark) by forming on the surface of the support medium a layer having an accurately known thickness.
Such conditions virtually do not exist in nature and it is to the merit of the inventors that they have discovered that by subjecting a geological formation sample to a neutron bombardment having appropriate energy, generally less than 1eV, the incoherent inelastic diffusion spectrum of the neutrons interacting with the material contained in the sample presents peaks corresponding to energy transfers, the value of the transferred energies being characteristic of certain materials contained in the geological formations. This energy transfer takes place from incident neutrons to certain molecules of the geological formations or conversely.
The inventors then studied the incoherent inelastic diffusion spectra of different geological samples whose composition had been determined by prior processes and established, for certain materials likely to be contained in geological formations, one or more reference values of the energy values for which the inelastic diffusion spectrum presents energy losses.
The method of the invention is advantageously applied to all kinds of organic materials, hydrocarbons, minerals, particularly argillaceous minerals, water and generally to hydrogenated materials.
In particular, it is possible to characterize the sedimentary hydrocarbons and organic materials in an oil reservoir or more generally in sedimentary rocks.
It is still within the scope of the present invention to apply it to the detection of other materials.
The present invention proposes subjecting geological formations to a bombardment by neutrons having a given energy and to detect in an incoherent inelastic diffusion spectrum of the energy of the neutrons reflected by the geological formations, the values of the energy ranges for which the spectrum presents peaks.
Each peak corresponds to a group of diffused neutrons having substantially the same energy. This energy is detected by the position of the peak in the spectrum. By comparing the value of the energies corresponding to the different peaks with the value of the energy of the incident neutrons, the amounts of elementary energies the most frequently transferred from the neutrons to certain molecules of the formations or conversely may be determined. By comparing these transferred elementary amounts with reference values, information may be inferred particularly qualitative information relating to the geological formations, such as the possible nature of certain materials contained in these formations. Tests have been carried out by using reference values close to 175 meV and/or 370 meV. By examining the size or intensity of the peaks, possibly of the incoherent elastic diffusion peak, the qualitative information may be confirmed, which was heretofore described, and/or quantitative information relating to some at least of the detected materials, such as the relative or absolute material contents may be obtained and information may be gathered relating to the density of protons or hydrogen atoms contained in the geological formations.
According to one particular embodiment of the invention, the presence of a material in the geological formations may be inferred from the analysis of the inelastic diffussion spectrum having one or more given energy values corresponding to the reference values established for this material.
The invention also provides a device for implementing the method for detecting the presence of certain materials in geological formations passed through by a drill hole.